Device to obtain stereoscopic effects in cinematographic projections



F. LEHNHOFF-WYLD.

DEVICE T0 OBTAIN STREOSCOPIC EFFECTSIN CINEMATOGRAPHIQFROJECTIONS.

APPLICATION FILEDAJAN.2I.19ZO.

F. LEHNHOFF-WYLE'.

DEVICE T0 OBTAIN STEREOSCOPIC EFFECTS IN CINEMATOGRAPHIC PROIECTIONS.

APPLICATION FILED IAN. 2|. 1920.

1,41 9 ,90 1 Patented June 13, 1922.

2 SHEETS-SHEET 2.

. UNITED STATES PATE-NT caricia.

rnnnnnrc Lmmnorr-WYLD, or rams, ramon DEVICE '.IOv OBTAIN STEREOSCOPIC EFFECTS IN CINEMATOGRAPHIC PROJECTIONS.

is characterized essentially by the fact thaty the image presented to the observers is projected by a suitable projecting apparatus on a convex and inclined screen which is reflected on a spherical mirror equally iiiclined; said convex screen, transparent or opaque, being arranged between the focus and the center of the concave mirror and permitting of obtaining a true enlarged luminous image, not reversed (inverted) and free from all distortions projected on the convex screen.

In accordance with this invention, use. is made, for the obtainment of cinematograpliic images with stereoscopic effects, of certain properties of the spherical mirrors which are otherwise considered as defects in the construction of some optical apparatus, such as telescopes, and the like.

For the same purpose, use is also made of the deformation of the image produced by the relatively considerable distance separating` the screen from the axis of the mirror:

or obtaining the rectification, that is the vertical aspect of the image reproduced in these conditions, the luminous image is suitabl inclined to the vertical plane.

1517i this manner, an enlarged virtual image is obtained, the ,stereoscopic effect of which results: from the strong deformation of the image in relation to the distanceseparating the screen from the axis of the mirror; from the lack of similitude of the image simultaneously seen by both eyes and rom the different distortions given to the image by the spherical mirror. y

The accompanying drawings diagrammatically illustrate, by way of example, two methods of application of the device forming` the subject-matter of the invention.

ig. 1 shows an arrangement in which the transparent screen as well as the projection apparatus are arranged below the plane of the spectators;

Fig. 2 illustrates an arrangement in which the transparent screen and the projecion apparatus are located" above the spectaors;

Figs. 3 and 4 relate to another arran ement in which the screen is opaque. In 1g. 3, this screen and the are located below the s ctators, w ilst in F1 .0 4 they are arrange above the latter.

ig. 5 is a theoretical view indicating how the image reflected according to the above mentioned principle is seen from different points of observation, by both eyes of an observer, for instance.

As will be seen in Figs. l to 4, the present device substantially comprises: an inclined spherical mirror a, a transparent or opaque screen b and a projection apparatus c of any suitable type.

The inclination of the spherical mirror a is determined in such manner that its main axis approximately forms the bisector of an angle, determined by a radius corre-y ,Specmcation ot Letterslatent. Patented June 13, 1922.` y Application filed January `y21, 1920. Serial No. 353,028.

projection ap aratus 'f by way of indication and. may be modified v -according to the available room and premises. Moreover, it will be noted, in these figures, that the transparent or opaque sci-'een b is always. arran ed between the focus F and the centre of t e mirror a, so as to pro; duce by reflection on the latter, `an enlar ed and noninverted virtual image d of the uminous scene projected by the projection apparatus c on the screen b whether the latter be transparent as in lgs. 1 and 2, or opaque as in Figs. 3 and 4.

In case the screen is opaque, Figs. 3 and 4, it is necessary to rectify the image in the lateral direction; the projectionapparatus c is, in this case, arranged, relatively to the screen b, on the same side as the mirror a with a rectifying prism.-

modified accprdin to the circumstances and to the space avai able; the saidscreen may be arranged either below the spectators (Figs. 1 and 3) or above as in Figs. 2 and 4 and on either side.

.The stereoscopicl effect is more particularly produced when observlng an,k ima e, Such as d, by the lack of slmitude of t e images simultaneously seen by both eyes,

but different for each eye considered sepai rately.

VTo each point of the screen object and. for each eye correspond two small focal lines; the geometrical locations of their middle-points constitute two different nna es of the screen object; the stereoscopic e ect depends on the preponderance taken by one or the other of these images for each eye, preponderance which .is the result of a sychological and unconscious action of selection. Y

By referring to Fig. 5, if we suppose, for instance, a Screen 'b and a spherical mirror a arranged as above mentioned, so as to obtain an enlarged virtual image d of the scene projected on the screen, it will be understood that a spectator the eyes 'of whom are indicated at e f will see that image in the followingmanner: A

The left eye e sees the left end b1 of the horizontal image at e1 and thel right end lb? of the same image at e?.

The'right eye f of the spectator sees the same points b1 and b2 of the image at f1 and f2 respectively. n

It will be understood that the image simultaneously observed by each of the eyes of the spectator differon several points. Flrst, the images e1 e2, f1 f2 do not'occu y the same plane, the image e1 e2 being arther away from the observer than the lm a e f1 2; moreover, this image f1 f2 whic 1s nearer, occuples a more open vlsual angle and appears enlarged. i

In fact, on this figure, the transverse dimensions are enlarged by the strongerdispersion of the rays coming from b2 and falling on the mirror nearer its ed e.

The deformation resulting'there rom for the reflected image, increases as one approaches its end f2 and is greater than that produced at e.

Both vimages e1 e2, f1 f2 diHer therefore more and more as the distance from the centre of the mirror increases and they do not overlap at all-at f2.

In this way the stereoscopic arallax necessary for the vision in relief is o tained.

Considerations similar to 'those above established for the visual points e f may also be determined for other points of the mirror a or for other visual points g h givv ing the im ression of the respective images g1 g2- and 1 h2 corresponding to the sides b1 b of the screen b, simultaneously observed by two visual rays starting from h and g.

The distortion given by the mirror to the reflected images causes the ends d2 of a square image d (supposed to be aplanatic) to be transferred, for instance at h2 (Fig. 5). If, as stated, we consider a square surface, the edges of the image and especially its four angles will be enlarged and drawn nearer the observer; as far as relief is concerned, we thus obtain an advantage which may still be increased by suitably inclining the plane of the luminous image. VThe edges of the images will thus appear as moving towards the observer which will largely contribute to give the effect of relief sought for by creating the sensation of distance.

The lack ofr coincidence of the two retinal images, which is one of the causes of the stereoscopic effect, gives another result when the dissimilitude regards not only the enlargement and size of the ima es, but more p.

specially the lack` of coinci ence of the planes they occupy, as well as of their lights and shades.

In this case, the luminous and shaded portions which do not exactly overlap give the im ression of the shining refiex, character istic of metallic objects, olished surfaces, water surfaces and the li e, and this sensation of lustre gives finally to the reproduction of the views obtained according to the above described device, their absolutel natural aspect and character. l The optica illusion `is completed] by other causes, arisin from a special effort of accommodation an coordination.

In the above described device, the ima seen in the spherical mirror resents a eformation of the horizontal lines which incline, more or less, at their ends, towards the side where the screen is located.,

For correcting this defect,.the screen instead of being plane as described, may posses a curved surface, which surface con stitutes a surface of revolution either spheri-y cal, ovoid, conical, or the like, according to the position of the screen.

This correction can also be effected by placing a suitably calculated lens in front of the projection apparatus or in front of the screen.

The application of the above device to entertainment halls, is obviously given only by way of example andit will be understood that, without departing from the sco of this invention, the forms, materials an sizes of the mirror and screen ma be modified according to the various con itions of application and to the available space, the sizes of these various parts mi ht be, for instance, sufficiently reduced for a lowing the constitution o'a device capable of being used in a drawing room for the production of stereoscopic effects in the same conditions as those above set forth.

Claim:

A device `for obtaining stereoscopic effects in cinematographic projections comprising in combination, a spherical inclined mirror, a screen arranged between the focus and the center of the mirror, a apparatus, said screen being Asuitably inclined to reect on the concave mirrorthe image projected by saidl apparatus and to obtain a true. and large -and notreversed' image ofv the scene V pro].ected on "the screen, Sald screen havin afconvex surface-to correct the deformations'of the horizontal lines f 'y rejecting The foregoing specification of device m allow-ing to obtain Vstereoscopic eects in cinematographicprojections in black and in colors, signed .by me. thisvlst day of December, 1919. l p

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